1. Field of the Invention
The present invention relates to a semiconductor device having a circuit including a thin film transistor (hereinafter referred to as a TFT) using an oxide semiconductor film for a channel formation region and a method for manufacturing the semiconductor device. For example, the present invention relates to an electronic appliance mounted with an electro-optic device typified by a liquid crystal display panel or a light-emitting display device having an organic light-emitting element as a component.
Note that the semiconductor devices in this specification refer to all the devices which can operate by using semiconductor characteristics, and an electro-optic device, a semiconductor circuit, and an electronic appliance are all included in the semiconductor devices.
2. Description of the Related Art
In recent years, active matrix display devices (such as liquid crystal display devices, light-emitting display devices, and electrophoretic display devices) in each of which a switching element including a thin film transistor (TFT) is provided in each of display pixels arranged in matrix have been actively developed. An active matrix display device is advantageous because a switching element is provided in each pixel (or each dot) and thus lower voltage driving is possible as compared to a passive matrix display device in the case where pixel density is increased.
In addition, a technique applied to an electronic device or an optical device, in which a thin film transistor (TFT) or the like is formed using an oxide semiconductor film for a channel formation region, has attracted attention. As an oxide semiconductor film, a TFT using ZnO and a TFT using InGaO3(ZnO)m are given for example. Patent Documents 1 and 2 and the like disclose a technique applied to a switching element or the like of an image display device, in which a TFT formed using such an oxide semiconductor film is formed over a substrate having a light-transmitting property.